A wheel adapter is a fork reduction sleeve: The reduction sleeve is designed to narrow the fork opening to ensure that if the tire ruptures, the rim never passes through the fork.
For models that do not have adjustable forks, wheel adapters/ reduction sleeves are available to lift vehicles with small wheels, such as vans and automobiles. Vehicles with wheel diameters from R-12 to R-15 require two wheel adapters/reduction sleeves per column. Vehicles with wheel diameters from R-15 to R-17 require one wheel adapter/reduction sleeve.